Mice placed in the center of an apparatus, the Elevated-Plus Maze, can choose to enter one of two types of alleys (or arms), an open alley or a closed alley, both of which are elevated significantly above the floor. This behavior can be quantified as the percentage of times an animal enters the open alley in comparison to the total number of entries into either the open or closed arms (%OpenArmEntries). %OpenArmEntries is assumed to reflect the balance between an animals drive to explore new areas and the fear (or anxiety) engendered by being in an open relatively more lit area. Two inbred strains, A/J and CBA/J, that differed widely in their Elevated Plus-Maze behavior were mated to generate two independent F2 generations of mice. A QTL (quantitative trait loci) analysis is being conducted using microsattelite markers and PCR. In addition recombinant inbred lines are being used to verify loci identified by the QTL analysis. - CBA/J, A/J, qtl, animal behavior